The present invention relates to data networking, telecommunication networking, and, in one embodiment, to systems and methods for extending the useful range of Fibre-Channel links.
The Fibre-Channel standard defines a bi-directional link protocol, used to connect computers to disk drives and other peripherals. A typical Fibre-Channel link may have a bandwidth of 1063 Mbps and a span of up to 10 kilometers.
One typical application of Fibre-Channel is interconnecting computer CPUs with arrays of disk drive in large scale computing centers, as would be used in, e.g., financial transaction processing. For reasons of fault tolerance, it is desirable to locate redundant storage resources at remote locations. The advent of high data rate metropolitan optical networks including such networks based on the use of dense wave division multiplexing (DWDM) and/or SONET/SDH transport systems makes it possible to extend so-called storage area networks (SANs) that carry multiple Fibre-Channel links over distances much longer than 10 kilometers.
It is useful to apply the widely prevalent Fibre-Channel standard to communicate across DWDM networks and therefore minimize the need to redesign computing center equipment. Such DWDM networks can themselves employ protocol such as Gigabit Ethernet, 10 Gigabit Ethernet, SONET, etc. A problem arises, however, in that most Fibre-Channel devices available now assume link distances of no more than 10 kilometers while it is desirable to locate SAN nodes much further apart, e.g., hundreds of kilometers.
The Fibre-Channel standard defines a flow control scheme that maximizes data throughput while preventing the transmitter from sending more data than the receiver is currently able to process. For the most prevalent classes of Fibre-Channel devices, the standard utilizes a buffer-to-buffer credit management scheme. When a link is set up, the two ends exchange information about the size of their receiver buffers. The remote receiver buffer size becomes an initial credit value that is decremented after every frame transmission. The remote Fibre-Channel port sends a ready signal indication after each received frame but only if sufficient buffer space has been cleared to accommodate the largest possible frame of new data. The transmitting port increments its credit value in response to the received ready signal indication. New frames are transmitted only when the credit value is positive. This scheme works well over relatively short distances but breaks down over larger distances because of the long delay between sending a frame and receiving a ready indication in response.
U.S. patent application Ser. No. 10/166,213 (not admitted as prior art) discloses a supplemental flow control scheme to facilitate Fibre-Channel operation over longer distances through, e.g., a SONET/SDH transport network. Each port terminating a Fibre-Channel link is connected to the transport network via a transport network interface. The transport network interface operates a supplemental buffer at the transport network egress to augment the capacity of the local Fibre-Channel port's buffer. To exploit the extra buffer capacity, a locally generated ready indication substitutes for the remotely generated ready indication provided by the Fibre-Channel standard. The locally generated ready indication is provided sooner than the remotely generated one so transmission can continue even though the remote ready response is delayed by the long propagation time. The supplemental buffer assures that the local Fibre-Channel port internal buffer will not be overrun.
It is not always desirable to locally generate ready signals. The above-described scheme will not accommodate all Fibre Channel traffic types. Alternative systems and methods for managing flow control in Fibre-Channel links that extend over large distances are needed.